Knife blade renewable cartridge fuse



Sept 17, 1957 DE'rcH KNIFE BLADE RENEWABLE CARTRIDGE FUSE Filed Nov. 12'; 1953 9 mm H F s INVENTOR. mimfi ATTORNEY United States Patent KNIFE BLADE RENEWABLE CARTRIDGE FUSE Lewis Detch, Pittsburgh, Pa.

Application November 12, 1953, Serial No. 391,500

12 Claims. (Cl. 200131) This invention relates to electric circuit breakers, particularly thermal current breakers, and more especially fusible element breakers of the well-known thermal type renewable cartridge form.

Those acquainted with the construction, operation and effects of the well known knife blade cartridge type fuse are well aware that the insulating bar commonly used to separate the knife blades a precise distance apart is subject to considerable deterioration, especially at the most important positions thereof, that is, at the very ends. This deterioration is due to the quite intense heat to which the insulating bar is often exposed. This intense heat frequently burns or carbonizes the ends of the insulating bar to such an extent that the material thereof crumbles away so that the disc abutting the shoulders of the knife blade and supposedly positioned a fixed predetermined distance apart by the insulating bar, are allowed a certain amount of free motion between the shoulders on the knife blade and the ends of the insulating bar. This free motion of the disc or washers prevents the proper tight closing of the interior of the fuse by the usual collars on the ends of the fuse. The net result is that the venting of the fuse is very seriously interfered with so that the hot gases and molten metal formed when the fuse is subjected to a short circuit current are not properly confined and may issue from the fuse in such manner as to easily ignite adjacent inflammable material.

It is also well known to those acquainted with knife blade cartridge fuses of the usual form that the pressure of the usual collars used for holding the knife blades and interior portions of the fuse in place causes a stress to be placed on the insulating bar tending to cause it to bend or bow and so tilt the usual knife blades in such a manner that they are not in one plane through the longitudinal center line of the fuse. As a consequence, it is often very difiicult to insert such fuses in the usual clip provided therefor.

It is a principal object of my invention to improve the construction of the usual knife blade cartridge fuse embodying an insulating spacer bar by providing a construction whereby the ends of the insulating spacer bar are not so easily deteriorated.

A further object of the invention is to provide a device of the type specified which will largely obviate the bending or bowing stress which is brought to bear in the usual cartridge fuse on the usual insulating spacer bar.

Other objects and advantages will appear as the description of the particular physical embodiment selected to illustrate the invention progresses and the novel features will be particularly pointed out in the appended claims.

In describing the invention in detail and the particular physical embodiment selected .to illustrate the invention, reference will be had to the accompanying drawings and the several views thereon,in which like characters of reference designate like parts throughout the several views, and in which:

Fig. l is a longitudinal sectional view of a knife blade cartridge fuse embodying my invention;

Patented Sept. 17, 1957 Fig. 2 is a fragmentary longitudinal sectional view of a cartridge fuse embodying my invention taken on a plane at a right angle to the plane upon which Fig. 1 is taken;

Fig. 3 is a cross sectional view of the device as shown by Fig. 1 on the plane indicated by the line III-III viewed in the direction of the arrows at the ends of the line;

Fig. 4 is a perspective view of an insulating bar attaching means or saddle used in my invention;

Fig. 5 is an edge view of a disc or washer;

Fig. 6 is a plan view of a washer or disc used as an end closure of a cartridge fuse construction in accordance with my invention;

Fig. 7 is a fragmentary view of a modified form of my invention showing one end of an insulating spacer bar and the closely adjacent parts;

Fig. 8 is a plan view of a knife blade and an associated disc formed in accordance with my invention;

Fig. 9 is a fragmentary view of a modified form of my invention showing one end of an insulating spacer bar with closely adjacent associated parts;

Fig. 10 is an elevational view of the right hand end of the device as shown by Fig. 8;

Fig. 11 is a cross sectional view of the device as shown by Fig. 9 on the plane indicated by the line XI-XI viewed in the direction of the arrows at the ends of the line;

Fig. 12 is a perspective view of a modified form of the device such as is shown by Fig. 4.

In the drawing, 1 designates a hollow cylinder formed of insulating material, preferably horn fiber.

Upon one end of the cylinder 1, a ferrule 3 is secured in any suitable or appropriate manner as by interengaging screw threads 5 and by the usual pin 7, best shown in Fig. 2. Ferrule 3 is preferably formed with an external screw thread 9 to cooperate with an internal screw thread 11 on a collar 13. This collar 13 has a flange 15 which is adapted to receive a washer or disc 17 and hold the disc from moving outwardly from the interior of the cylinder 1.

The other end of the cylinder 1 may be arranged in any suitable or appropriate manner. An external screw thread 19 may be formed thereon to cooperate with an internal screw thread 21 in a collar 23 provided with a flange 25' adapted to cooperate with and retain washer or disc 27 from moving outwardly from the interior of the cylinder 1.

Within the cylinder 1 here is an insulating spacer bar 29. This spacer bar has through bores 31 in each end thereof and in the through bores a bolt 33 is positioned passing through a through bore 35 in a knife blade 37 and through a fusible strip 39. The bolt 33 is provided with a nut 41 so that the insulating spacer bar 29, knife blade 37 and the fusible strip 39 are held tightly together. The construction at one end of the fuse is preferably the same as the construction at the other end of the fuse insofar as the connection between the spacer bar and the knife blade is concerned although I do not want it to be understood that I must necessarily have the same construction at each end although I have shown the same construction at each end of Fig. l.

The constructions hereinbefore described are old and well known and it is an object of the present invention to improve the construction because of the effects thereof.

In improving the present construction, applicant prefers to separate the ends of the insulating bar 29 from the disc or washers as 17 and 27 leaving a space at each end such as 43. The usual construction is to have the end of insulating bar 29 bear firmly against a member corresponding to 27. I may have my insulating bar bear against the disc 27, but I prefer to have it separated therefrom.

The object of having bar 29 at its end bear against washer 27 in conventional construction is so that when collar 23 is brought down against washer 2'7 there will be a tight joint because washer 27 bears firmly against the end of insulating bar 29, and if the other end of insulating bar 29 bears firmly against the inside surface of disc 17 and collar 13 is in place, the distance between the insidefaces of discs 17 and 27 is proper in connection with the length of bar 29 so there will be a tight joint between the collars and the discs so that any gases formed Within the cartridge will issue slowly so that no adjacent material will be likely to be burned.

In my construction, instead of having a washer, such as 27, abut directly on the end of an insulating bar 29, 1 have it abut a tongue 45 which passes through a slot 47 in the knife blade 37. The disc therefor bears firmly against thetongue 45 onone side and bears tightly against shoulders 49, as best shown in Fig. 2, on the other side. Thus, the washer or disc, such as 27, is firmly and precisely held in position so that it cannot wobble or have any free movement whatsoever. As the fuse is used there can be no lost motion or other motion gained by the disc 27 because it is held between metal surfaces, as the knife blade 37 which is of metal, preferably copper, and the tongue 45 which is of metal. 7

When a collar, as 23, is screwed down in place against a disc, as 27, when my construction is used, the pressure is brought against knife blade 37 by pressure against tongue 45 which is right along the longitudinal center line of the knife blade and on equal portions thereof on each side of the longitudinal center line, and this stress is trahsrnitted to a bolt, as 3.3, which acts to transmit the stress along the longitudinal center line of insulating bar 29 and on the equal areas on each side theerof.

In order to make the transmission of forces more perfect and in order to prevent the insulating bar 29 from getting out of hue with the knife blade 37, I extend the tongue 45 to a plane portion 51, shown in Fig. 1 and also well shown in Fig. 4. I also form flanges 53 and 55, one on each side of the plane portion 51, and I make the dimensions such that -the flanges 53 and 55 are just far enough apart to closely receive the insulating bar 29, as well shown in Fig. 3, so that the bar is restrained from getting out of line with the knife blades, as 37.

I also prefer to extend the flanges 53 and 55, as shown in Fig. 4, so that I have prongs 57 and 59, and these prongs are made just long enough so that they extend out into the plane of the outer face 61 of the tongue 45 so that they assist i'n holding the disc 27 tightly against the shoulders; as '49, on the knife blade, as 37.

In order to hold themember 60 illustrated in Fig. 4 and which I call a saddle, in proper position in relation to the ends of the insulating bar 29, I form a through bore '62, through the plane portion 51 and have the bolt 33 pass therethrough.

In order to further increase the rigidity of the connection between insulating bar 29 and the saddle, I form a through bore through each end of the insulating bar 29 and insert a pin, as 65, therethrough which also passes through the plane portion of the saddle so that I may form, as a unitary device, an insulating bar, as 29, with a saddle at each end attached firmly thereto by means of pins, as 65, or other suitable connection so that if the insulating bar of a fuse does become inoperative to perform its functions, I may remove it and replace it with a new insulating or 'space'r bar equipped with a saddle at each end thereof, the saddle having the outer faces of the tongues the precise distance apart in order to properly perform their intended function. The tongue 45 of saddle 60 thus not only serves the function of keeping spacer bar 29 spaced from the washers or discs 17, 2 7, but also seals the slots 17E, 27E in the respective discs 17, 27 through which the knife blades 37 extend, to the extent that when the fusible strip 39 is volatilized 4 the escape of gases or molten metal through the slots 17E, 27B is materially retarded.

I may make my disc or washer 27 with a plane uninterrupted periphery but I prefer to form the periphery as illustrated by Figs. 5 and 6 in which the periphery is formed with what might be called teeth, as 67 and 69. The outer face of these teeth would be slightly separated from the surface 71 of a collar, as 23, or the internal surface 73 of a ferrule, as 3, so that the space between teeth, as 67 and 69, such as 75, would allow an easier exit for gases and molten metal than the form of disc as shown by 27.

I may increase the rigidity of the connection between the tongue of my saddle and the adjacent disc on the knife blade by forming a tongue receiving groove, as 77, in the washer and also by pinning the tongue, as 45, to the washer by means of a pin, as 79.

in Figs. 9, ll and 12, I have shown a modification of my saddle. This saddle is shown in perspective in Fig. 12. It has a plane portion 81 corresponding to the plane portion 51 of the saddle as shown by Figs. 1 and 4. It also has the side flanges 83 and 85 corresponding to the other saddle and a tongue 87 bent at a right angle to the plane portion 81 just as the tongue 45 of Fig. 4 is bent at a right angle to the plane portion 51 of the saddle of Fig. l. The modified form of saddle shown by Figs 9, 11 and 12 also has prongs as 89 and 91 corresponding to the prongs 57 and 59 of Fig. 4 and in addition has two additional tongues 93 and 95 which are both bent at a right angle to the plane portion 81, and the outer faces of tongues 87, 93 and 95 are also in the same plane as the ends of prongs 89 and 91.

The tongue 87, as best shown in Fig. 11, passes through a slot 97 in the knife blade 99 and the tongues 93 and 95 each lie on opposite sides of the knife blade 99 so that the knife blade cannot get out of line sidewise with the saddle, shown as a whole by Fig. 12.

In Figs. 8 and 10 I have shown a modified form of washer 101. This washer has a slot 103 in it as shown by Fig. 10 into which the tang end 105 of the knife blade 107 passes and on each edge of the knife blade 107 and the tang 105 are positioned projections or nubs 109, 111, 113 and 115. When the tang end of the knife blade has been placed through the washer 101, the nubs or projections may be peened down in close contact with the knife blade thereby preventing the quick and easy exit of gases and molten metal along the joints between the disc or washer 103 and the knife blade 107 and the tang 105.

The washers or discs 17 and 27 are made preferably with three circumferential surfaces, as 17A, 17B, 17C, Figure 2. This facilitates assembly.

Surface 17B being of larger diameter and centrally located, and surfaces 17A and 17C being of equal length and diameter, the washers 17, 27 are symmetrical end to end and cannot be wrongly assembled no matter which end is in or out.

A further advantage of washers 17 and 27 as illustrated is particularly useful in case of short circuit of a heavy duty fuse, such as 600 ampere rating. The explosion inside the fuse casing is very powerful. The additional mass is located inside the circumferential surface 17 C. Surface 17C, being in spaced relation to the surfaces 71, 73 is exposed to the hot gases, but constitutes an impenetrable barrier to the gas, which therefore exerts pressure against the opposed surfaces 71 or 73 which are also impenetrable.

The shoulders 17D between the large diameter surface 17B and the small diameter surface 17A, on either side thereof afford an excellent seat for the collars 13 and 23 giving a good tight joint at the point to suitably retard the exit of hot metal and vapors.

Although I have particularly described one particular physical embodiment of my invention and explained the construction and principle thereof, nevertheless, I desire to have it understood that the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent is:

and a through slot and a shoulder, two metallic electrically and thermally conducting discs, one on each knife blade abutting the shoulder thereof, two metallic electrically and thermally conducting saddles, one at each end of the said bar, each saddle including a portion resting against the bar, a prong at one end of each saddle adapted to abut a disc on one of said knife blades, a tongue on each saddle formed at a right angle to the portion of the saddle resting against the bar, said tongue adapted to lie in the slot of one of said knife blades, each said saddle formed with a through bore in the portion resting against the bar, two bolts, each bolt passing through a through bore in the bar and through a through bore of said saddle and through a through bore of one of said knife blades, and a nut on each bolt.

2. The device as specified in claim 1 including means for attaching said saddle fixedly to said bar.

3. The device as specified in claim 1 including a pin passing through the bar and the portion of the saddle resting against. the said bar attaching the saddle to the bar.

4. The device as specified in claim 1 in which the saddle includes two flanges, one at each side of the portion resting against the bar, the said bar resting therebetween.

5. The device as specified in claim 1 in which the saddle is formed with a plurality of tongues, all lying with their outer faces in the same plane and that plane the plane in which the end of the prong lies.

6. The device as specified in claim 1 in which the tongue includes means for fastening it to the disc on one of said knife blades.

7. In a cartridge fuse, an insulating spacer bar, two metallic knife blades, one positioned at each end of the spacer bar and each formed with a through slot, a metallic saddle positioned between each knife blade and the spacer bar, said saddle including a plane portion resting on one side against one of said knife blades and on the other side against the spacer bar, said saddle further formed with upturned edges resting against the sides of the spacer bar, said saddle further formed with a tongue projecting at a right angle to the said plane portion, and positioned in a slot of one of said knife blades, and bolts, one passing through and attaching each end of the spacer bar and one of said saddles to one of said knife blades.

8. A cartridge fuse blades spacer including, in combination, an elongated insulating bar formed with a through bore at one end, an electrically conducting knife blade positioned at the end of the said bar, said knife blade formed with a through slot, and with a shoulder, an electrically and thermally conduct-ing disc on the knife blade abutting the shoulder thereof, an electrically and.

thermally conducting saddle positioned at the end of the said bar, said saddle including .a portion resting against the bar, a prong at one end of the saddle adapted to abut the disc on the knife blade, a tongue formed at a right angle to the portion of the saddle resting against the bar, said tongue adapted to lie in the slot of the knife blade, said saddle formed with a through bore in the portion resting against the bar, a bolt, said bolt passing through a through bore in the bar and through a through bore of said saddle.

9. A knife blade and closure for a cartridge fuse including an electrically and thermally conducting knife blade of substantially fiat form having the width reduced at one end forming two shoulders and a tang end, an electrically and thermally conducting disc, said disc formed with a through slot receiving a tang of the knife blade with the shoulders on the knife blade resting against the disc, projections on both sides of the disc adjacent both edges of the knife blades, said projections lying in peened closeness to the knife blade whereby flow of gases along the edges of the knife blade and slot is impeded.

10. In a knife blade cartridge fuse of the type having a hollow cylinder of insulating material, collars at each end of said cylinder, means fastening said collars to said cylinder, a disc abutting each collar on the inside of the latter, said disc being formed with a slot, a knife blade extending through said slot, and an insulating spacer bar connected to both of said knife blades, said knife blades, said discs and said Washers being electrically and thermally conductive, each of said knife blades further being formed with a slot therethrough and located interiorly of said cylinder and adjacent said discs, the improvement comprising a saddle, a saddle comprising a plane portion lying between said spacer bar and one of said knife blades and a tongue integral with said plane portion and extending at a right angle thereto and through said slot of said last mentioned knife blade and sealing said slot of said disc.

11. In a knife blade cartridge fuse of the type having a hollow cylinder of insulating material, means closing one end of said cylinder and formed with a slot, a collar detachably connected to the other end of said cylinder, a washer abutting said collar inside said cylinder and formed with a slot, a knife blade extending through each of said slots, said means, said washer and said knife blades being thermally and electrically conductive, the improvement comprising an insulating spacer bar formed adjacent each end thereof with a through bore, a metallic electrically and thermally conducting saddle at each end of said spacer bar, said saddle having a plane portion located between said spacer bar and one of said knife blades, said plane portion formed with a through bore in registry with one of said bores of said spacer bar, said knife blades further being formed with a through bore, said knife blades further being formed with a slot extending therethrough and located interiorly of said cylinder adjacent said washer and said means respectively, said saddles further each having a tongue extending substantially perpendicularly to said plane portion and through the respective slots of said knife blades and sealing said slots of said washer and said means respectively, bolts extending through said bores of said spacer bar, said saddles and said knife blades, and nuts on said bolts and connecting together said spacer bar, said saddles and said knife blades.

12. The device as specified in claim 1 in which one of said saddles is provided with an additional tongue extending parallel to said first mentioned tongue and against the side of the adjacent knife blade.

References Cited in the file of this patent UNITED STATES PATENTS 1,092,153 Mallory Apr. 7, 1914 1,540,119 Glowacki June 2, 1925 1,702,355 McDonald et al Feb. 19, 1929 1,845,756 La Mar Feb. 16, 1932 1,907,739 Clark May 9, 1933 2,079,097 Wood May 4, 1937 2,198,663 Floten Apr. 30, 1940 2,521,600 P-flaum Sept. 5, 1950 

